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          11_文件上传下载
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        <h3 id="1-准备工作"><a href="#1-准备工作" class="headerlink" title="1. 准备工作"></a>1. 准备工作</h3><p>文件上传是项目开发中最常见的功能之一，Spring MVC 可以很好的支持文件上传，但是Spring MVC 上下文中默认没有装配<code>MultipartResolver</code>，因此默认情况下其不能处理文件上传工作。如果想使用 Spring 的文件上传功能，则需要在上下文中配置<code>MultipartResolver</code>。</p>
<p>前端表单要求：为了能上传文件，必须将表单的<code>method</code>设置为<code>post</code>，并将<code>enctype</code>设置为<code>multipart/form-data</code>。只有在这样的情况下，浏览器才会把用户选择的文件以二进制数据发送给服务器；</p>
<p><strong>对表单中的<code>enctype</code>属性做个详细的说明：</strong></p>
<ul>
<li><code>application/x-www=form-urlencoded</code>：默认方式，只处理表单域中的 value 属性值，采用这种编码方式的表单会将表单域中的值处理成 URL 编码方式。</li>
<li><code>multipart/form-data</code>：这种编码方式会以二进制流的方式来处理表单数据，这种编码方式会把文件域指定文件的内容也封装到请求参数中，不会对字符编码。</li>
<li><code>text/plain</code>：除了把空格转换为<code>+</code>外，其他字符都不做编码处理，这种方式适用直接通过表单发送邮件。</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">form</span> <span class="attr">action</span>=<span class="string">&quot;&quot;</span> <span class="attr">enctype</span>=<span class="string">&quot;multipart/form-data&quot;</span> <span class="attr">method</span>=<span class="string">&quot;post&quot;</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;file&quot;</span> <span class="attr">name</span>=<span class="string">&quot;file&quot;</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;submit&quot;</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">form</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>一旦设置了<code>enctype</code>为<code>multipart/form-data</code>，浏览器即会采用<strong>二进制流</strong>的方式来处理表单数据，而对于文件上传的处理则涉及在服务器端解析原始的 HTTP 响应。</p>
<ul>
<li>Servlet3.0 规范已经提供方法来处理文件上传，但这种上传需要在 Servlet 中完成。</li>
<li>而 Spring MVC 则提供了更简单的封装。</li>
<li>Spring MVC 为文件上传提供了直接的支持，这种支持是用即插即用的<code>MultipartResolver</code>实现的。</li>
<li>Spring MVC使用<code>Apache Commons FileUpload</code>技术实现了一个<code>MultipartResolver</code>实现类<code>CommonsMultipartResolver</code>。因此，Spring MVC 的文件上传还需要依赖<code>Apache Commons FileUpload</code>的组件。</li>
</ul>
<span id="more"></span>

<h3 id="2-文件上传"><a href="#2-文件上传" class="headerlink" title="2. 文件上传"></a>2. 文件上传</h3><ol>
<li><p>导入 jar 包</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">dependency</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">groupId</span>&gt;</span>commons-fileupload<span class="tag">&lt;/<span class="name">groupId</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">artifactId</span>&gt;</span>commons-fileupload<span class="tag">&lt;/<span class="name">artifactId</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">version</span>&gt;</span>1.4<span class="tag">&lt;/<span class="name">version</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">dependency</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">dependency</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">groupId</span>&gt;</span>javax.servlet<span class="tag">&lt;/<span class="name">groupId</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">artifactId</span>&gt;</span>javax.servlet-api<span class="tag">&lt;/<span class="name">artifactId</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">version</span>&gt;</span>4.0.1<span class="tag">&lt;/<span class="name">version</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">dependency</span>&gt;</span></span><br></pre></td></tr></table></figure>
</li>
<li><p>配置 bean（固定格式）</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">&lt;!-- 文件上传配置 --&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">bean</span> <span class="attr">id</span>=<span class="string">&quot;multipartResolver&quot;</span>  <span class="attr">class</span>=<span class="string">&quot;org.springframework.web.multipart.commons.CommonsMultipartResolver&quot;</span>&gt;</span></span><br><span class="line">    <span class="comment">&lt;!-- 请求的编码格式，必须和jsp的pageEncoding属性一致，以便正确读取表单的内容，默认为ISO-8859-1 --&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;defaultEncoding&quot;</span> <span class="attr">value</span>=<span class="string">&quot;utf-8&quot;</span>/&gt;</span></span><br><span class="line">    <span class="comment">&lt;!-- 上传文件大小上限，单位为字节（10485760=10M） --&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;maxUploadSize&quot;</span> <span class="attr">value</span>=<span class="string">&quot;10485760&quot;</span>/&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">property</span> <span class="attr">name</span>=<span class="string">&quot;maxInMemorySize&quot;</span> <span class="attr">value</span>=<span class="string">&quot;40960&quot;</span>/&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">bean</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p><code>CommonsMultipartFile</code>的常用方法：</p>
<ul>
<li><code>String getOriginalFilename()</code>：获取上传文件的原名</li>
<li><code>InputStream getInputStream()</code>：获取文件流</li>
<li><code>void transferTo(File dest)</code>：将上传文件保存到一个目录文件中</li>
</ul>
</li>
<li><p>编写页面</p>
<figure class="highlight jsp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">&lt;form action=<span class="string">&quot;$&#123;pageContext.request.contextPath&#125;/upload&quot;</span> enctype=<span class="string">&quot;multipart/form-data&quot;</span> method=<span class="string">&quot;post&quot;</span>&gt;</span><br><span class="line">  &lt;input type=<span class="string">&quot;file&quot;</span> name=<span class="string">&quot;file&quot;</span>/&gt;</span><br><span class="line">  &lt;input type=<span class="string">&quot;submit&quot;</span> value=<span class="string">&quot;upload&quot;</span>&gt;</span><br><span class="line">&lt;/form&gt;</span><br></pre></td></tr></table></figure>
</li>
<li><p>编写控制器（固定格式）</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> com.horsen.controller;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> org.springframework.stereotype.Controller;</span><br><span class="line"><span class="keyword">import</span> org.springframework.web.bind.annotation.RequestMapping;</span><br><span class="line"><span class="keyword">import</span> org.springframework.web.bind.annotation.RequestParam;</span><br><span class="line"><span class="keyword">import</span> org.springframework.web.multipart.commons.CommonsMultipartFile;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServletRequest;</span><br><span class="line"><span class="keyword">import</span> java.io.*;</span><br><span class="line"></span><br><span class="line"><span class="meta">@Controller</span></span><br><span class="line">   <span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">FileController</span> &#123;</span><br><span class="line">       <span class="comment">/**</span></span><br><span class="line"><span class="comment">        * 将name=file控件得到的文件封装成CommonsMultipartFile对象</span></span><br><span class="line"><span class="comment">        * 批量上传CommonsMultipartFile则为数组即可</span></span><br><span class="line"><span class="comment">        */</span></span><br><span class="line">       <span class="meta">@RequestMapping(&quot;/upload&quot;)</span></span><br><span class="line">       <span class="keyword">public</span> String <span class="title function_">fileUpload</span><span class="params">(<span class="meta">@RequestParam(&quot;file&quot;)</span> CommonsMultipartFile file, HttpServletRequest request)</span> <span class="keyword">throws</span> IOException &#123;</span><br><span class="line">           <span class="comment">//获取文件名: file.getOriginalFilename();</span></span><br><span class="line">           <span class="type">String</span> <span class="variable">uploadFileName</span> <span class="operator">=</span> file.getOriginalFilename();</span><br><span class="line">           <span class="comment">//如果文件名为空, 直接回到首页</span></span><br><span class="line">           <span class="keyword">if</span> (<span class="string">&quot;&quot;</span>.equals(uploadFileName)) &#123;</span><br><span class="line">               <span class="keyword">return</span> <span class="string">&quot;redirect:/index.jsp&quot;</span>;</span><br><span class="line">           &#125;</span><br><span class="line">           System.out.println(<span class="string">&quot;上传文件名: &quot;</span> + uploadFileName);</span><br><span class="line">           <span class="comment">//上传路径保存设置</span></span><br><span class="line">           <span class="type">String</span> <span class="variable">path</span> <span class="operator">=</span> request.getServletContext().getRealPath(<span class="string">&quot;/upload&quot;</span>);</span><br><span class="line">           <span class="comment">//如果路径不存在，创建一个</span></span><br><span class="line">           <span class="type">File</span> <span class="variable">realPath</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">File</span>(path);</span><br><span class="line">           <span class="keyword">if</span> (!realPath.exists()) &#123;</span><br><span class="line">               realPath.mkdir();</span><br><span class="line">           &#125;</span><br><span class="line">           System.out.println(<span class="string">&quot;上传文件保存地址: &quot;</span> + realPath);</span><br><span class="line">           <span class="comment">//文件输入流</span></span><br><span class="line">           <span class="type">InputStream</span> <span class="variable">is</span> <span class="operator">=</span> file.getInputStream();</span><br><span class="line">           <span class="comment">//文件输出流</span></span><br><span class="line">           <span class="type">OutputStream</span> <span class="variable">os</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">FileOutputStream</span>(<span class="keyword">new</span> <span class="title class_">File</span>(realPath, uploadFileName));</span><br><span class="line">           <span class="comment">//读取写出</span></span><br><span class="line">        <span class="type">int</span> <span class="variable">len</span> <span class="operator">=</span> <span class="number">0</span>;</span><br><span class="line">           <span class="type">byte</span>[] buffer = <span class="keyword">new</span> <span class="title class_">byte</span>[<span class="number">1024</span>];</span><br><span class="line">           <span class="keyword">while</span> ((len = is.read(buffer)) != -<span class="number">1</span>) &#123;</span><br><span class="line">               os.write(buffer, <span class="number">0</span>, len);</span><br><span class="line">               os.flush();</span><br><span class="line">           &#125;</span><br><span class="line">           os.close();</span><br><span class="line">           is.close();</span><br><span class="line">           <span class="keyword">return</span> <span class="string">&quot;redirect:/index.jsp&quot;</span>;</span><br><span class="line">       &#125;</span><br><span class="line">   <span class="comment">/**</span></span><br><span class="line"><span class="comment">    * 采用file.Transto来保存上传的文件</span></span><br><span class="line"><span class="comment">    */</span></span><br><span class="line">   <span class="meta">@RequestMapping(&quot;/upload2&quot;)</span></span><br><span class="line">   <span class="keyword">public</span> String <span class="title function_">fileUpload2</span><span class="params">(<span class="meta">@RequestParam(&quot;file&quot;)</span> CommonsMultipartFile file, HttpServletRequest request)</span> <span class="keyword">throws</span> IOException &#123;</span><br><span class="line">   </span><br><span class="line">       <span class="comment">//上传路径保存设置</span></span><br><span class="line">       <span class="type">String</span> <span class="variable">path</span> <span class="operator">=</span> request.getServletContext().getRealPath(<span class="string">&quot;/upload&quot;</span>);</span><br><span class="line">       <span class="type">File</span> <span class="variable">realPath</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">File</span>(path);</span><br><span class="line">       <span class="keyword">if</span> (!realPath.exists()) &#123;</span><br><span class="line">           realPath.mkdir();</span><br><span class="line">       &#125;</span><br><span class="line">       <span class="comment">//上传文件地址</span></span><br><span class="line">       System.out.println(<span class="string">&quot;上传文件保存地址: &quot;</span> + realPath);</span><br><span class="line">   </span><br><span class="line">       <span class="comment">//通过CommonsMultipartFile的方法直接写文件（注意这个时候）</span></span><br><span class="line">       file.transferTo(<span class="keyword">new</span> <span class="title class_">File</span>(realPath + <span class="string">&quot;/&quot;</span> + file.getOriginalFilename()));</span><br><span class="line">   </span><br><span class="line">       <span class="keyword">return</span> <span class="string">&quot;redirect:/index.jsp&quot;</span>;</span><br><span class="line">   &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></li>
</ol>
<h3 id="3-文件下载"><a href="#3-文件下载" class="headerlink" title="3. 文件下载"></a>3. 文件下载</h3><ol>
<li><p>设置 response 响应头</p>
</li>
<li><p>读取文件 – InputStream</p>
</li>
<li><p>写出文件 – OutputStream</p>
</li>
<li><p>执行操作</p>
</li>
<li><p>关闭流 （先开后关）</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@RequestMapping(&quot;/download&quot;)</span></span><br><span class="line"><span class="keyword">public</span> String <span class="title function_">downloads</span><span class="params">(HttpServletResponse response , HttpServletRequest request)</span> <span class="keyword">throws</span> Exception&#123;</span><br><span class="line">    <span class="comment">// 要下载的图片地址</span></span><br><span class="line">    <span class="type">String</span>  <span class="variable">path</span> <span class="operator">=</span> request.getServletContext().getRealPath(<span class="string">&quot;/upload&quot;</span>);</span><br><span class="line">    <span class="type">String</span>  <span class="variable">fileName</span> <span class="operator">=</span> <span class="string">&quot;test.png&quot;</span>;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 1. 设置response响应头</span></span><br><span class="line">    <span class="comment">// 设置页面不缓存, 清空buffer</span></span><br><span class="line">    response.reset();</span><br><span class="line">    <span class="comment">// 字符编码</span></span><br><span class="line">    response.setCharacterEncoding(<span class="string">&quot;UTF-8&quot;</span>);</span><br><span class="line">    <span class="comment">// 二进制传输数据</span></span><br><span class="line">    response.setContentType(<span class="string">&quot;multipart/form-data&quot;</span>); </span><br><span class="line">    <span class="comment">// 设置响应头</span></span><br><span class="line">    response.setHeader(<span class="string">&quot;Content-Disposition&quot;</span>,</span><br><span class="line">                       <span class="string">&quot;attachment;fileName=&quot;</span>+ URLEncoder.encode(fileName, <span class="string">&quot;UTF-8&quot;</span>));</span><br><span class="line">    <span class="type">File</span> <span class="variable">file</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">File</span>(path,fileName);</span><br><span class="line">    <span class="comment">// 2. 读取文件--输入流</span></span><br><span class="line">    InputStream input=<span class="keyword">new</span> <span class="title class_">FileInputStream</span>(file);</span><br><span class="line">    <span class="comment">// 3. 写出文件--输出流</span></span><br><span class="line">    <span class="type">OutputStream</span> <span class="variable">out</span> <span class="operator">=</span> response.getOutputStream();</span><br><span class="line"></span><br><span class="line">    <span class="type">byte</span>[] buff =<span class="keyword">new</span> <span class="title class_">byte</span>[<span class="number">1024</span>];</span><br><span class="line">    <span class="type">int</span> index=<span class="number">0</span>;</span><br><span class="line">    <span class="comment">// 4. 执行写出操作</span></span><br><span class="line">    <span class="keyword">while</span>((index= input.read(buff))!= -<span class="number">1</span>)&#123;</span><br><span class="line">        out.write(buff, <span class="number">0</span>, index);</span><br><span class="line">        out.flush();</span><br><span class="line">    &#125;</span><br><span class="line">    out.close();</span><br><span class="line">    input.close();</span><br><span class="line">    <span class="keyword">return</span> <span class="literal">null</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

 <figure class="highlight jsp"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">&lt;a href=<span class="string">&quot;$&#123;pageContext.request.contextPath&#125;/download&quot;</span>&gt;点击下载&lt;/a&gt;</span><br></pre></td></tr></table></figure></li>
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